1. Field of the Invention
The present invention relates to solid-state imaging devices, and particularly, to a solid-state imaging device that includes an electrode pad on a foreside of a semiconductor substrate and underside wiring extending through the semiconductor substrate from an underside of the semiconductor substrate so as to be connected to the electrode pad.
2. Description of the Related Art
As a small-size optical sensor device, a solid-state imaging device has been reported, which is formed by bonding a transparent substrate onto a peripheral region of an imaging-area face of a chip-size semiconductor substrate with a sealant, forming a through hole that extends from an underside of the semiconductor substrate to an electrode pad extending around the imaging-area face, and then forming underside wiring by filling the through hole with a conductive material. Specifically, in order to form solid-state imaging devices of the aforementioned type, a transparent substrate is first bonded onto a wafer. Then, after forming the underside wiring, the transparent substrate and the wafer are segmented into pieces so that each device is formed into a chip-size package. Examples of such a solid-state imaging device are disclosed in Japanese Unexamined Patent Application Publication No. 2005-202101 and in Preprint for Association of Super-Advanced Electronics Technologies (ASET): SEMI Forum Japan 2005, p. 46 (JISSO Seminar, Jun. 7, 2005, SEMI Japan).
An example of a solid-state imaging device of the related art will be described below with reference to FIG. 8. A solid-state imaging device 10 shown in FIG. 8 includes a transparent substrate 22 and a semiconductor substrate 11 that are bonded to each other with a sealant 21 therebetween. The semiconductor substrate 11 has thereon an imaging area S having an array of optical sensors and an electrode pad 12 extending from the imaging area S.
The imaging area S is provided at a central section on a foreside of the semiconductor substrate 11. The semiconductor substrate 11 has an insulating film 13 composed of, for example, silicon oxide (SiO2) disposed thereon. The electrode pad 12 is disposed on the insulating film 13 and extends along the periphery of the semiconductor substrate 11. The electrode pad 12 is formed of, for example, a thin aluminum (Al) film having a thickness of about several hundreds of nanometers.
The semiconductor substrate 11 and the insulating film 13 have a through hole 14 that extends from the electrode pad 12 to an underside 11a of the semiconductor substrate 11. An insulating film 15 is provided on the underside 11a of the semiconductor substrate 11 and covers the sidewalls of the through hole 14. At the underside of the semiconductor substrate 11, underside wiring 16 formed of a copper (Cu) film with a thickness of several tens of micrometers is provided, such that the underside wiring 16 covers the inner walls of the through hole 14 covered with the insulating film 15.
An underside-protection resin 17 is provided above the underside wiring 16 and the insulating film 15 and is embedded in the through hole 14. The underside-protection resin 17 is given an opening 17a through which the underside wiring 16 is exposed. The underside wiring 16 exposed through this opening 17a has a bump 18 disposed thereon, which serves as an external connection terminal.
On the other hand, the sealant 21 is composed of an organic insulating material having adhesion properties and is formed to a thickness of several tens of micrometers on a side of the semiconductor substrate 11 where the electrode pad 12 is disposed. With this sealant 21, the transparent substrate 22 formed of a glass plate is bonded to the semiconductor substrate 11.